When apps like VidUp want to access YouTube accounts, they need to do it over the YouTube Data API (application programming interface). For this API you need an API account with login credentials which have nothing to do with your Google/YouTube account login credentials. This API account with its login credentials belongs to the app and all users using this app (or other apps with the same API account) share these credentials.
The problem is that the access to the API is limited, every API account has a quota limitation per day and every request vs. the API costs some amount of quota. When the quota is used up, no one will be able to send requests to the API until the quota is reset once a day. Which means you can’t use the app(s) anymore that use this API account. This is where the annoying „VidUp’s YouTube access is closed for today (API quota exceeded).“ errors come from.
By default an API account has 10,000 quota. Normal requests to get some data of the API, e.g. getting a playlist information cost 1 quota, adding something to YouTube via the API, e.g. create a new playlist or adding videos to a playlists costs 50 quota. But uploading a video costs 1,600 quota! So with a newly created API account you can upload 6 videos a day. Maybe enough for one user, but surely not for hundreds of users.
Currently VidUp has 1,000,000 quota which is shared by all users, but even this does not seem enough. I see the „VidUp’s YouTube access is closed for today (API quota exceeded)“ errors every day. I requested a quota extension, but the problem will come back on a regular basis I guess, so with the new version I have implemented the possibility to use your own API credentials. As I said a new API login is limited to about 6 uploads a day, but that should be enough for most of the users.
I also prepared a guide how to create your own API account/credentials.